Operational Radiation Protection in Radiotherapy Flashcards Preview

Y3: Radiation Safety in Radiotherapy > Operational Radiation Protection in Radiotherapy > Flashcards

Flashcards in Operational Radiation Protection in Radiotherapy Deck (37)
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Name 2 radiation sources in radiotherapy and state the dose rate from that source.

-CT imaging - 0.3 mSv/s in bore centre
-SXT unit - 80 mSv/s at applicator
-Brachytherapy unit - 5000 mSv/s adjacent to source
-Linac unit - 250 mSv/s at beam portal


What are the risks to workers from therapeutic beams?

-Member of staff remains in the bunker during treatment.
-Maintenance staff work close to Klystron with HT on. (Klystron is radiation source)
-Radiographic staff regularly exposed to low level induced radioactivity in linac head.
-Maintenance staff work close to linac head following high energy exposure.
-For multiple source rooms, unintended exposure from ‘the other source’.


What are the risks to a MoP from therapeutic beams?

They may remain within the bunker during beam on without staff knowledge


What is in place to reduce the risks to staff & MoPs from therapeutic beams?

-CCTV in the bunker
-Emergency stops
-Control of access


What does control of access do in terms of radiation protection?

-Ensures only patient is in the bunker
-Establishes who has authority over access (operator in charge)


What are common access rules?

Local rules common to many areas.
(then have a set of local rules for that specific area)


What binds a radiation worker to following local rules?

It is a condition of employment.


What does 'handing over control' of a room entail?

-SOPs will be different
-Local rules will change
-The responsible employer will change
-Equipment responsibility will change


What does an RT specific handover form contain?

-Formal removal from clinical service to prevent use prior to arrival of service engineer.
-Explicit statement on service agency LRs (have you seen their local rules)
-Requires statement of work (to enable local decision on appropriate QC)


What are the 3 types of safety controls in RT, and give 2 examples of each?

Engineering controls:
-Search buttons (incl button timing)
-Fail-safe door interlock

Procedural controls:
-Operator in control
-Last person out executes search button sequence
-Exposure initiator responsible for checking room empty
-Room monitoring (cameras, intercom)

Personal protective equipment:
-TLD badge
-Source handling tools


What is the purpose of each type of safety control in RT? (name and explain all 3)

Engineering – take away possibility of procedural error – design to fail safe = test this regularly.
Procedural – will one day go wrong as involves people remembering to do it
PPE – badge – prevents person from working with radiation if close to limit (future safety control – rather than immediate)


What is the purpose of beam on indicators and emergency stops?

Reduce the extent of accidental exposure if it happens.

Indicators and emergency stops in a number of places inside and outside the room that aim to move a person away from MV radiation (kV radiation buttons normally only on equipment itself).


What is the need for PPE based on?

Surveys taken from around the working beam. (environmental surveys as well as commissioning surveys).


What is the dose limit for non-radiation employees?

1 mSv (same as MoP)


What does IRR99 state about QA for RT?

Employer shall:
…make arrangements for a suitable quality assurance programme …for the purpose of ensuring that [the equipment] remains capable of restricting so far as is reasonably practicable exposure to the extent that this is compatible with the intended clinical purpose or research objective.


What does the IRR99 ACOP state about QA for RT?

[For radiotherapy equipment], the aims of medical exposure are rather different and the QA programme should clearly be designed to support those aims. Important features of the programme are likely to include:
(a) initial and periodic calibration of radiation equipment and dosemeters; and
(b) constancy checks of the geometrical aspects of external therapy machines and simulators, beam uniformity, timers, and source positioning devices.


What legislation is required for sealed sources?

-Radioactive Substances Act (RSA 93)
-Environmental Permitting Regulations (EPR 2010)
-Medicines (Administration of Radioactive Substances) regulations (MARS 1978)


What is the purpose of the radioactive substances act?

It is a registration for the keeping and using of radioactive substances.
It gives authorisation for accumulation and disposal of radioactive waste.
Need to register if using check sources, HDR source or low activity brachytherapy seeds.


What is the purpose of the environmental permitting regulations?

To use or dispose of radioactive sources, must have a permit from environment agency.
Need High Activity Sealed Source (HASS) permit for micro-selectron


What is the purpose of the Medicines (Administration of radioactive Substances) regulations?

Certificate to administer medicinal radioactivity – Issued by Administration of Radioactive Substances Advisory Committee (ARSAC).


What advice is given to patients with implanted LDR seeds?

-How soon can spend time in contact with others
-Information on triggering airport sensors
-What to do if a seed is passed in urine


What does the card given to LDR implant patients contain?

Proof of legitimate radioactivity.
Dates for safe activities.
Contact numbers for enquiries.


What is the radiation weighting factor for photons?



What is the limit of a controlled area?

7.5 uSv/hr


What are the three principles of radiation protection?

Time, distance, shielding.


What is the primary barrier?

The part of the barrier that the Linac can directly point at.
It will be thicker and more attenuating than the secondary barrier.


How is the width of the primary barrier determined?

The largest field size with the collimator at 45 degrees. This covers the full extent of where the primary beam may go.


What does the secondary barrier stop?

Scattered radiation.


What is the main source of scattered radiation?

Head leakage.
Designing the secondary barrier for head leakage should account for any other sources of scatter.


What percentage of the primary beam is head leakage allowed to be?

=< 0.1 %